A so-called easy open end has heretofore been widely used as a container end that can be easily unsealed by hand without using any particular utensils. From the standpoint of workability, the container end is made of a metal blank such as a tin plate, a surface-treated steel plate like TFS or a resin-coated metal plate obtained by coating an aluminum alloy with a resin coating such as a polyester film, the container end made of the above metal plate being provided with a score extending in the way in the direction of thickness of the metal plate so as to sectionalize a portion for opening. A rivet is formed by the end plate in the portion for opening, a pull-tab is fixed by the rivet, and the end is double-seamed with the flange such as a can body member.
An easy open end of this kind has been proposed being made of a composite member comprising an aluminum substrate, a biaxially drawn polyethylene terephthalate film of a thickness of 10 to 40 μm on a side of the substrate that becomes the inside of a can made of the aluminum substrate, and an epoxy-phenol resin type adhesive primer layer of a thickness of 0.3 to 3 μm interposed between the aluminum substrate and the film, and having a score formed in the aluminum substrate extending in the way in the direction of thickness thereof (JP-A-62-52045).
The easy open end of the type of stay-on tab (SOT) is opened by pushing in the end of a tab for opening and cutting the score. The opening operation causes the score to be cut in a manner that the resin layer on the inner surface side of the laminated board stretches giving rise to the occurrence of delamination between the metal blank and the inner resin layer. Therefore, the metal blank is cut and, thereafter, the resin layer is cut being deviated in time, and the user feels it stiff and sticky to open the end but may not feel the end is lightly opened.
Particularly, a canned product packing soup, coffee, black tea or green tea is in many cases heated in hot water or in a hot vendor, and is opened. In this case, the inner resin layer is in a state where it can be easily stretched, and the above tendency becomes conspicuous.
To solve the above problem, there has been proposed an easy open end which can be favorably opened and, particularly, even at high temperatures by selecting a difference between the mountain and the valley (maximum height of roughness) on the side of the metal blank that becomes the inner surface of the container to lie in a range of 0.05 to 20 μm and selecting a bubble area ratio to be not larger than 30% in the interface between the metal blank and the resin layer (JP-A-11-124134).